The present disclosure relates generally to light emitting devices and, more particularly, to techniques for using wavelength conversion materials with light emitting devices.
The present disclosure is directed to optical devices. The disclosure provides a light source that includes two or more layers of phosphor materials excited by radiation sources that emit radiations in two or more wavelengths, with at least one of the radiation wavelength less than 440 nm. In a specific embodiment where LED radiation sources are used, LED radiation sources that emit ultra-violet (UV), violet (V), or near-ultraviolet (NUV) radiation are used to excite blue phosphor material. In various embodiments, red and green phosphor materials are used and the LED radiation sources are arranged in a specific pattern. In other embodiments red, green, and blue phosphor materials are used.
In the late 1800's, Thomas Edison invented the light bulb. The conventional light bulb, commonly called the “Edison bulb”, has been used for over one hundred years. The conventional light bulb uses a tungsten filament enclosed in a glass bulb sealed in a base, which is screwed into a socket. The socket is coupled to an AC power or DC power source. The conventional light bulb can be found commonly in houses, buildings, and outdoor lightings, and other areas requiring light. Unfortunately, drawbacks exist with the conventional Edison light bulb. That is, the conventional light bulb dissipates much thermal energy. More than 90% of the energy used for the conventional light bulb dissipates as thermal energy. Additionally, the conventional light bulb eventually fails due to evaporation of the tungsten filament.
Fluorescent lighting overcomes some of the drawbacks of the conventional light bulb. Fluorescent lighting uses an optically clear tube structure filled with a noble gas, and typically also contains mercury. A pair of electrodes is coupled between the gas and to an alternating power source through ballast to excite the mercury. Once the mercury has been excited, it discharges, emitting UV light. Typically, the optically clear tube is coated with phosphors, which are excited by the UV light to provide white light. Many building structures use fluorescent lighting and, more recently, fluorescent lighting has been fitted onto a base structure, which couples into a standard socket.
Solid state lighting techniques are also known. Solid state lighting relies upon semiconductor materials to produce light emitting diodes (LEDs). At first, red LEDs were used. Modern red LEDs use Aluminum Indium Gallium Phosphide (AlInGaP) semiconductor materials. Most recently, Shuji Nakamura pioneered the use of InGaN materials to produce LEDs emitting light in the blue color range for LEDs. The blue light LEDs led to innovations such as solid state white lighting, the blue laser diode, the Blu-Ray™ DVD player, and other developments. Blue-, violet-, or ultraviolet-emitting devices based on InGaN are used in conjunction with phosphors to provide white LEDs. Other colored LEDs have also been proposed.
One way of improving solid state light efficiency has been to use phosphor converted LEDs (pcLED) technology, where an LED emits radiation that excites phosphors, which in turn emit light. Unfortunately, conventional pcLEDs have been inadequate, especially for white light for general illumination applications. In particular, blue-excited pcLED configurations have the challenge that blue light leakage must be managed to provide a stable white output. This is difficult because blue light leakage depends on the peak emission wavelength which shifts with drive current and operating temperature. V- or NUV-excited pcLEDs avoid this problem, but have performance disadvantages due to increased Stokes' loss, as well as cascading conversion loss, since much of the V or NUV light pumps blue phosphor, which then excites green and red phosphors, rather than direct excitation of the green and red phosphors.
Therefore, it is desirable to have improved techniques for phosphor-based LED devices.